Bought mine with 12k 3 years ago, now it's at 33k. So I guess that works out to around 7k a season on average. I usually get to ride from May- October.
Though one year I had like 11k, and one year it rained all summer and I had a lot less so it wasn't quite even. I'm already at like 5k this year, though that's mostly due to commuting to work on my bike, which is 90 miles round trip 6 days a week.
People like to make a big deal out of how many miles they ride every year. I guess it can be kind of funny with some of the weekend warrior HD types who have a 5 year old bike and 2000 miles on it making jokes about "real" riders, but in the end if you're out enjoying yourself IMO mileage is pretty irrelevant. Not everyone has the time to log tens of thousands a year, and some riding is better than none.